1. Field of the Invention
The invention relates to a capacitive sensing array device and an electronic apparatus using the same, and more particularly to a capacitive sensing array device with high sensitivity and an electronic apparatus using the same.
2. Related Art
The conventional capacitive sensing technology for sensing the skin of the human body may be applied to, for example, the fingerprint sensor for sensing finger's textures or a capacitive touch panel or a capacitive touch screen.
More particularly, the basic structure of the portion of the sensor in contact with the skin's texture to sense the skin's texture is an array-type sensing member. That is, several sensing members with the same structures constitute a two-dimensional array sensor. When a finger is placed on the array sensor, for example, the ridge of the finger's texture is in direct contact with the array sensor, and the valley of the finger's texture is separated from the array sensor by a gap, so that the two-dimensional capacitive image of the finger's texture may be captured, and this is the basic principle of the capacitive skin texture sensor.
In the most frequently seen sensing member structure, due to the electroconductive property of the human body, the skin in contact with the sensor may be regarded as an equal-potential electrode plate and each sensing member may be regarded as a plate electrode, so that a capacitor is formed between each sensing member and the skin. The materials disposed between the electrode plates include the cuticle on the surface of the finger's skin and a sensor protection layer disposed on the sensing electrode and in contact with the skin. The protection layer may be a single insulating layer or may contain multiple insulating layers and must have the environment-corrosion-resistant property, the impact-resistant property, the wearing-resistant property, the electrostatic-discharge-resistant property and the like.
In order to achieve the above-mentioned properties of the protection layer, one direct method is to increase the thickness of the protection layer. However, the too-thick protection layer causes the very small sensing capacitance, thereby decreasing the sensitivity.
FIG. 1 is a schematic illustration showing an assembled structure of a conventional capacitive fingerprint sensor 500. As shown in FIG. 1, the conventional capacitive fingerprint sensor 500 is usually manufactured in two stages. In the first stage of manufacturing a fingerprint sensing chip 510, semiconductor manufacturing processes are utilized to form sensing members 514 and chip bonding pads 515 on a semiconductor substrate 511, and then a chip protection layer 512 is formed on the sensing members 514 to provide the protective and impact-resistant properties. In the second stage, which is a packaging stage, the fingerprint sensing chip 510 is placed on a package substrate 520, multiple wires 530 are bonded to the chip bonding pads 515 and package bonding pads 525 by way of wire bonding, and than a package protection layer (or referred to as a molding compound layer) 540 is provided to cover the wires 530 and the bonding pads 515 and 525, and only the region with the sensing member array is exposed. Such conventional package processes require a special mold and a special process flow to protect the sensing member region from being covered by the molding compound and need a special machine. So, the cost is high.
In the existing IC wire-bonding technology, the distance from the chip surface 513 to the package surface 523 is greater than or equal to about 100 microns (um). Taking the fingerprint sensor with the specification of 500 DPI as an example, the area of each sensing member 514 is about 50 um×50 um. If the molding compound is to deploy on the sensing member, according to the dielectric constant of the commercial molding compound, the calculated capacitance of the sensing member is smaller than about 1 fF, which is too small to design a sensing circuit. If the thickness control of the package substrate, the thickness control of the chip and the like are considered at the same time, this distance further causes the great sensing error.
Thus, the conventional package protection layer 540 cannot be disposed above and cannot cover the sensing member 514. So, the chip protection layer 512 has to be formed in the first stage, and the thickness (about 1 to 20 microns) of the chip protection layer 512 cannot be too thick to affect the sensing capacitance. Consequently, in addition to the high cost, it is a great challenge to the requirements on the environment-corrosion-resistant property, the impact-resistant property, the wearing-resistant property, the electrostatic-discharge-resistant property and the like of the sensor.
FIG. 2 is a schematic illustration partially showing sensing electrodes of a conventional capacitive fingerprint sensor 600. As shown in FIG. 2, in addition to the sensing capacitor Cf between each sensing electrode 610 of the capacitive fingerprint sensor 600 and the finger F, a parasitic capacitor Cp1 is present when viewed from the sensing electrode 610 to the inside of the chip. In addition, because the sensor device is an array device having a plurality of sensing members, a parasitic capacitor Cp2 is also present between each of the sensing electrodes 610 and each of its neighboring sensing electrodes 610. These parasitic capacitors are in the fluctuating states. This non-constant parasitic capacitor interferes with the measurement, and is one of the main reasons of the incapability of achieving the high sensitivity. In order to achieve the sensitivity of Cf smaller than 1 fF, the solution of the interference between Cp1 and Cp2 is the most important issue.